Many applications are known in the art of drive couplings which utilize features of the prior art Oldham shaft coupling to connect opposed coaxial or offset parralel members or shafts for rotation at constant relative phase angles about their respective axes. Couplings of this type are shown for example in U.S. Pat. Nos. 1,244,533 and 1,171,347 Morse and 2,932,255 Neukirch. All these constructions utilize intermediate members connecting the opposed ends of members or shafts rotatable on parallel axes by opposed straight guides such as projections or tongues and grooves, keys and slots, rollers and guides and others. These guide means limit lateral motion of the intermediate members with respect to their connected members to straight paths whose axial projections intersect at right angles and cause rotation of the shafts while maintaining a fixed phase angle between them.
In U.S. Pat. No. 4,332,148 issued June 1, 1982 in the names of E.R. Maki and F. Freudenstein and assigned to the assignee of the present invention, a novel phase change coupling arrangement is disclosed which combines the simplicity of the prior Oldham coupling with novel modifications that provide rotation on offset parallel axes of connected elements with a cylic phase change variation. This Maki-Freudenstein phase change device differs from the generalized form of the prior Oldham coupling in that connection of an intermediate member with opposed members rotatable on offset parallel axes is accomplished by curved path guide means intersecting at an arbitrary selected angle rather than the right angled straight guide means of the Oldham coupling. To distinguish it from the straight guide Oldham coupling, I have referred to this novel phase change device as a "curved guide coupling".
In operation of a curved guide coupling, the phase angle change may be made adjustable from zero to a predetermined maximum by allowing variation of the displacement of the offset rotational axes of the connected end members. The form and amount of phase angle variation is determined in part by the selected phase angle between the curved path guide means and by the curvatures of those guide means. The circular arc form of the mechanism is kinematically equivalent to a four bar linkage as will be subsequently more fully discussed.